Where’s all my CPU and memory gone? The answer: Slack

Matthew O'Riordan
3 min readJul 27, 2017


TLDR; If you care about battery life or availability of your finite CPU and memory on your computer, then you probably won’t want to use Slack desktop with more than one or two accounts. Slack resource usage increases linearly as you add more accounts, and it quickly adds up.

28 July update: One of the Slack developers got in touch and recommended I try out their latest beta version in which the CPU issue appears to have been fixed. See below.

I’ve recently joined a few more Slack groups, outside my core business Ably’s team account, to chat with old colleagues, the tech community and even our recent investors and their portfolio companies.

I noticed that my machine has been sluggish and its battery life has become poor. Whilst investigating this, it turns out that Slack desktop fails badly when used with multiple accounts. This is because CPU and memory usage increases linearly as you add more accounts to your Slack desktop client. As a result, I believe the growing trend to use Slack to be part of multiple communities is seriously flawed until Slack resolve this problem.

The numbers:

Note: I am running a Slack desktop client on OS X with eleven (11) accounts.

Where’s all my CPU gone? The answer: Slack (76%)

CPU usage, 5% for each account consistently. 76.4% CPU time in total.

Where’s all my memory gone? The answer: Slack (1.5GB)

Memory usage, circa 50MB — 300MB for each account

Where’s all my battery power gone? The answer: Slack (60–70%)

Energy usage, circa 60–70% of entire host, all the time even when in the background

Here’s what happens when use only two accounts instead of eleven

Energy usage, circa 15–20% of host when accounts reduced to two. Reclaimed circa 50%

I love Slack and have no plans to stop using it to communicate with my team at Ably. However, given that the non-essential accounts I have added have turned my computer into a dog, I’m now using Slack only for essential communication. I think it’s time we all found a better tool for community chat. Bring back IRC I say :)

28 July update: One of the Slack developers got in touch and recommended I try out their latest beta version. Here’s how the CPU graph looks now with around 7 accounts:

CPU usage is nice and low when idle in beta 2.7.0

As you can see, the CPU issue is indeed fixed. I expect this fix will make it to the stable release soon. Thanks Slack!

Matthew O’Riordan, CEO, Ably



Matthew O'Riordan

Co-founder of Ably: Simply better realtime messaging. In the past was the CTO & co-founder of Econsultancy that was sold in 2012.